Langzeittelemetrie der K?rpertemperatur mit synchroner Bestimmung des Energiestoffwechsels beim Blaunackenmausvogel (Urocolius macrourus) unter Normal- und Lethargiebedingungen (Torpor)

Ohne Zusammenfassung

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Long-term telemetry of body temperature with synchronous measurement of metabolic rate in torpid and non-torpid Blue-naped Mousebirds (Urocolius macrourus)

     

In vitro analysis of mutant LexA proteins with an increased rate of specific cleavage.

Specific cleavage of LexA repressor plays a crucial role in the SOS response of Escherichia coli. In vivo, cleavage requires an activated form of RecA protein. However, previous work has shown that the mechanism of cleavage is unusual, in that the chemistry of cleavage is probably carried out by residues in the repressor, and not those in RecA; RecA appears to facilitate this reaction, acting as a coprotease. We recently described a new type of lexA mutation, a class termed lexA (IndS) and here called IndS, that confers an increased rate of in vivo cleavage. Here, we have characterized the in vitro cleavage of these IndS mutant proteins, and of several double mutant proteins containing an IndS mutation and one of several mutations, termed Ind-, that decrease the rate of cleavage. We found, first, that the autodigestion reaction for the IndS mutant proteins had a higher maximum rate and a lower apparent pKa than wild-type LexA. Second, the IndS mutations had little or no effect on the rate of RecA-mediated cleavage, measured at low protein concentrations, implying that the value of Kcat/Km was unaffected. Third, the rate of autodigestion for the double-mutant proteins, relative to wild-type, was about that rate predicted from the product of the effects of the two single mutations. Finally, by contrast, these proteins displayed the same rate of RecA-mediated cleavage as did the single Ind- mutant protein. We interpret these data to mean that the IndS mutations mimic to some extent the effect of RecA on cleavage, perhaps by favoring a conformational change in LexA. We present and analyze a model that embodies these conclusions.     

Chronopharmacokinetics and Cardiovascular Effects of Nifedipine

Orcadian phase dependency in pharmacokinetics and hemodynamic effects on blood pressure and heart rate of different galenic formulations of nifedipine (immediate-release, sustained-release, and i.v. solution) were studied in healthy subjects or in hypertensive patients. Pharmacokinetics of immediate-release but not sustained-release and i.v. nifedipine were dependent on time of day: immediate-release nifedipine had higher C_max (peak concentration) and shorter t_max (time-to-peak concentration) after morning than evening application, and bioavailibility in the evening was reduced by about 40%. Orcadian rhythm in estimated hepatic blood flow as determined by indocyanine green kinetics may contribute to these chronokinetics. A circadian time dependency was also found in nifedipine-induced effects on blood pressure and heart rate as monitored by 24-h ambulatory blood pressure measurements. In conclusion, the dose response relationship of oral nifedipine is influenced by the circadian organization of the cardiovascular system as well as by the galenic drug formulation.     

Neurophysiology of the vibration sense in locusts and bushcrickets: Response characteristics of single receptor units

The response characteristics of the vibration receptors in the legs of the migratory locust, Locusta migratoria, and the tettigoniid Decticus verrucivorus were investigated electro-physiologically by single cell recordings. The legs were stimulated by sinusoidal vibrations. There are four types of vibration receptor in each leg of Locusta and Decticus, which can be classified physiologically. One type—most probably campaniform sensilla—shows a phase-locked response to vibrations from 30 to 200 Hz, its threshold reflecting the displacement. A second type shows similar responses in the same frequency range, but its reactions depend on the stimulus acceleration. The receptor cells of the subgenual organ are very sensitive to vibration from 30 to at least 5000 Hz, and their responses depend on acceleration. There are two types of subgenual receptors, one of which shows a clear maximum of sensitivity between 200 and 1000 Hz, with a threshold below 0.01 m/sec^?2 acceleration. Subgenual receptors with different thresholds and different characteristic frequencies occur in each leg. The receptors of each leg pair have quite similar mean sensitivities and characteristic frequencies. However, in the front legs of tettigoniids the more sensitive subgenual receptors and an additional receptor type also respond to low-frequency airborne sound up to 10 kHz.     

Predominance of gonadotropin α-subunit resulting from preferential loss of hCGβ production in an established cell line

Summary The BeWo line of trophoblastic cells, maintained in continuous culture since 1966, was employed to investigate the phenomenon of gonadotropin α-subunit predominance that exists in several cell lines. The secretion of complete human chorionic gonadotropin (hCG) relative to α-subunit was compared in several different BeWo sublines, all of which were derived from BeWo stock roller tube colonies. In all of the BeWo sublines, secretion of hCG originally exceeded secretion of α-subunit. With time in culture, however, there was a marked decline in production of hCG/hCGβ, but not in α-subunit. Thus it appears that the production of hCGβ by BeWo choriocarcinoma cells is more labile than the production of the α-subunit.     

The reaction of the mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] with guanosine and cysteine

The mutagen 1,1′-hexamethylene-bis[(5-p-chlorophenyl)-biguanide] reacts at 37°C with guanosine and guanine to yield xanthosine or xanthine and oxidizes cysteine to cystine. After treatment of a guanosine-labelled DNA sample from Escherichia coli with the mutagen xanthine could be detected as a reaction product. At a slow rate the mutagen is hydrolysed spontaneously yielding urea, 1,6-hexanediol and 4-chloroaniline. The reaction mechanisms both of the hydrolysis and of the reaction with cysteine and guanosine are discussed.